Conventional spring-loaded electrical contact probes generally include an outer structure or barrel, a movable plunger slidably disposed within the barrel, and a spring within the barrel for biasing the reciprocating travel of the plunger within the barrel. A portion of the plunger is commonly biased outwardly away from the barrel a selected distance by the spring, and may be biased or depressed into the barrel, a selected distance, under force directed against the spring.
The spring and plunger are arranged in such conventional spring probes with the spring disposed within the barrel between a closed end of the barrel and an enclosed end of the plunger. Constructed in this manner, the barrel is sized having a length adapted to accommodate therein both the entire length of the spring and a portion of the plunger. The plunger is disposed within the barrel a sufficient length to provide a desired degree of tip alignment and stability, to minimize tip wobble and thereby ensure that a tip portion of the plunger that extends from the barrel is capable of making contact with the target electrical contact. Accordingly, the overall length of the barrel and plunger assembly making up the probe has been relative long to accommodate both the spring and a portion of the plungers sufficient to minimize plunger wobble.
When used in portable-type applications, including battery-powered articles, such as a portable computer, cellular phone and the like, the probe serves to make electrical contact with terminals or contacts of a removable electrical power source, such as a battery. The barrel portion of the probe is fixedly mounted within the battery-powered article so that contact between the probe plunger and the electrical contacts of the battery causes the plunger to be displaced within the barrel.
Electricity transmitted from the electrical source, e.g., battery, through such a conventionally configured probe to the battery powered article is conducted primarily through the spring. This is due to the relatively sporadic contact made between the side walls of the plunger and the surrounding inside wall of the barrel, and the resulting sporadic electrical continuity between them. Conventional probes are designed to facilitate free axial displacement of the plunger within the barrel. Accordingly, as the plunger is displaced in and out within the barrel, or moved laterally when loaded in a fixed axial position in the barrel, the adjacent plunger and barrel walls move in and out of contact with one another. This creates sporadic open circuits through the probe and causes the electrical current to be transmitted by the probe through the spring.
The wire diameter of springs used in conventional spring probes varies between approximately 0.1 to 0.3 millimeters and therefore limits the amount of current conducted through the spring. This effectively limits the application of such spring probes to low electrical current transfer applications. For example, such conventional spring probes are commonly used in applications where less than about 5 amperes of current are conducted, making such spring probes impractical for use in such high-current applications as portable computers and the like.
It is generally desired that the size of such battery powered portable devices be as small as possible to enhance portability. The trend has, therefore, also been to reduce both the size of the battery packs that power such devices and the related size of the batter pack ports in the battery-powered articles. In view of such size reductions, electrical spring-probes used to facilitate electrical connection between such battery-powered articles and battery packs used to power them also must be reduced.
It is, therefore, desired that a spring probe be constructed having a compact barrel and plunger design that will facilitate use in applications where reduced probe length and plunger travel are needed. It is desired that the spring probe be designed so that, while having reduced overall probe length, it maintains a desired degree of tip alignment, thereby minimizing plunger wobble. It is also desired that the probe be constructed with a sufficient degree of electrical contact between the barrel and plunger to provide a desired degree of electrical continuity to facilitate use in relatively high-current transfer applications.